The invention relates to a process for protecting roller bearings against corrosion, involving coating the surface and curing the coating on the bearings.
Roller bearings and their surrounding parts are often employed in an environment in which they are exposed to aggressive media. For example, the wheel bearings of motor vehicles are subjected in winter to aggressive stress from water spray and from grit, which leads to severe rust formation and may reduce the service life of the bearing. Although some roller bearings are made from stainless steel, those are too expensive for many applications.
DE 41 42 313 A1 discloses a roller bearing which is provided with an anticorrosion coating of a zinc alloy. The protective coating is applied by electroplating, before the bearing is assembled and before it is installed in its surrounding part. Consequently, that part must likewise be coated. The electroplated coating is not only laborious and expensive to apply, but the coating gives rise to environmental problems and also adversely affects the steel microstructure of the roller bearing through hydrogen embrittlement.
Coating with powder or wet coating materials, for protecting a wide variety of products against corrosion is likewise known in the art. In this case, the parts are sprayed with or immersed in the coating material, and the material is subsequently cured fully or it is baked in a hot oven. Dependent upon the product, the oven temperature is 200.degree. C. or more. For ready mounted and greased roller bearings provided with a seal, however, heat treatment of this kind is unsuitable, since there is a concern that the seals and the grease will be damaged in the process and that microstructural changes will occur in the roller bearing steel.
Finally, WO 93/24242 discloses a powder coating process in which the workpiece is heated by an inductor and the inductively heated workpiece is then sprayed with a coating powder, which is melted on. This process gives an anodic protective coat which is not electrically conductive and which is sensitive to subsequent scratches in the surface, causing rust creep. For reasons set out above, this process is likewise regarded as unsuitable for roller bearings.